1. Field of the Invention
The present invention relates to scene imaging systems and more particularly to a monitoring system for monitoring the required operation of an imaging sensor of the scene imaging system. The present monitoring system has particular application relative to monitoring an Enhanced Vision System (EVS) of an aircraft.
2. Description of the Related Art
Many devices, such as aircraft, are typically designed to provide a real-world view of the out-the-window scene for at least one operator to operate the device. In the past, a view of the scenery outside the device was provided through passive means, such as a cockpit windshield, or artificial means through sensors and displays.
Enhanced Vision Systems (EVS) supplement out-the-window vision via the use of camera/sensor imagery superimposed over the real-world view. EVS include sensors that can detect and display images of objects that pilots would not normally be able to see when looking through the cockpit window of an aircraft. For example, EVS can present data from sensors that can penetrate low-visibility weather conditions and darkness, such as radar or forward-looking infrared (FLIR). The data presented from the sensors is derived from the current environment and not from a computer database. EVS can be used on both head-down and head-up displays. Other features such as navigation enhancements and proactive systems to avoid controlled flight into terrain and runway incursions can also be integrated in EVS.
To achieve lower minima landing credit using an Infrared (IR) based EVS system, the integrity of both the IR sensor and display device (e.g., a Head Up Guidance System) must meet minimal integrity requirements based on the function being performed. To qualify for use during low visibility operations, the EVS Sensor and image fusion processor of the Head Up Guidance System (HGS) computer must not have any failure modes which would result in a hazardous failure condition for the aircraft. Therefore, a monitor may be required to independently monitor the sensor output for certain faults. The monitor must be designed to assure that no hazardous failure mode is undetected.
To achieve this level of integrity, the hardware must meet minimum Mean Time Between Failures (MTBF) and Built In Test (BIT) coverage requirements, and the software/firmware must be developed with a process that provides the appropriate level of integrity assurance. The issue that often arises in the development process, if a process was followed at all, is due to minimal or nonexistent design and design and performance assurance documentation. Either, portions of the development process must be performed again to establish this documentation, or monitoring techniques must be employed in the system which externally assures the required performance of the system and, therefore, alleviates the need for certain design documentation.
As will be disclosed below, the present invention provides a means to externally monitor the integrity of the EVS Sensor. The monitor is developed to an integrity level adequate to meet the end-to-end system requirements. It obviates the need to develop the EVS Sensor software/firmware to a specific avionics assurance level, and allows COTS software/firmware to be used without modification. This reduces the overall development costs and provides wider options in terms of sensor selections.